The present invention relates to inspection of semiconductor wafers and in particular to an apparatus and a method to automatically inspect for contamination, cracks, scratches and the like on a backside of a semiconductor wafer.
Conventional manufacture of semiconductor devices may generally be viewed as comprising three processes, i.e., semiconductor wafer fabrication, package assembly and test. The semiconductor wafer fabrication process creates integrated circuits or devices in and on a wafer surface. The wafer fabrication process may be carried out by repetition of many steps such as diffusion, photolithography, thin film formation and etching. After fabrication, the wafer may be sent to a wafer sawing procedure, which may divide the wafer into individual semiconductor chips. Next, each of the individual semiconductor chips may be assembled into a package by package assembly process.
Before the wafer sawing step, the wafer is normally inspected. The inspection generally checks the wafer backside for presence of contamination, cracks, scratches and the like, which may have been introduced during the semiconductor wafer fabrication process. Such contamination or other degradation might damage or adversely affect subsequent processes of the wafer. Conventionally, a wafer backside inspection has been performed manually and inspected visually. For example, an operator may manually grip the wafer and inspect the wafer by the “naked eye.”
It may be apparent that such visual inspection may not be reliable because of its dependence on the readiness and availability of the operator. In addition, a lot of time and human resource may be required for such inspection. Furthermore, as manufacturing flows more toward larger diameter wafers, e.g., moving from eight-inch to twelve-inch wafers, a reliability of such visual inspection by operators may drop.
The visual inspection may also be noted to provide an opportunity for recontamination, such as, e.g., scratching of the wafer surface due to inappropriate gripping by an operator.
The visual inspection may present further difficulties when trying to systematically manage the information which may result from the wafer backside inspections. Such information has conventionally been obtained by manually collecting and analyzing the results of the wafer backside inspections. In some instances, a photograph may be taken of the wafer backside. Such manually collected information resulting from the inspections might then be used to adjust some of the upstream procedures of the wafer fabrication process. However, these operations that have been required to collect and return the information to affect the upstream processes have conventionally imposed a heavy burden on the operators.